The present invention relates generally to electrical plug and jack connectors and, more particularly, to low profile connectors including jacks adapted to be inserted into printed circuit boards and modular type plugs designed for use therewith.
The termination of multi-conductor cord by modular type plugs has become commonplace especially in the telephone industry. Examples of such modular plugs are disclosed in various patents, such as U.S. Pat. Nos. 3,699,498, 3,761,869, 3,860,316 and 3,954,320. Another advantageous configuration of a moldular plug is disclosed in U.S. Pat. No. 4,211,462 assigned to Stewart Stamping Corporation, assignee of the instant application. Essentially, a modular plug includes a dielectric housing having a cavity into which an end portion of the cord is received. Flat contacts corresponding in number to the number of cord conductors are driven into respective slots which open at one of the housing sides and which are aligned with the conductors so that portions of the contacts form solderless connections with respective cord conductors. Straight edges of the contacts are exposed at the side of the housing in position for engagement by respective jack contacts when the plug is inserted into the jack.
It is becoming more commonplace to couple the conductors of multi-conductor cables to printed circuit boards by modular type plugs which terminate the cable. Accordingly, jacks for modular plugs have been designed specifically for connection to printed circuit boards.
Conventional jacks of this type, such as those available from Virginia Plastics Company of Roanoke, VA, generally comprise a one-piece plastic housing having a longitudinal cavity adapted to receive the modular plug. Asssociated with the housing are a plurality of jack contacts adapted to engage the straight edges of the plug contact when the plug is inserted into the jack receptacle. Each jack contact is held by slots or grooves formed in the jack housing and includes a portion which extends along the rear housing wall and projects below the bottom of the jack housing for insertion into the printed circuit board and a portion which extends through a slot formed through the jack housing top wall into the jack receptacle for engagement with the edge of a respective contact of the plug.
Jacks of this type are not entirely satisfactory for several reasons. For example, the jack contacts are exposed externally of the jack both at the rear as well as at the top wall thereof thus subjecting the contacts to possible damage during use. Moreover, portions of the jack contacts tend to be pushed out or become loosened from the slots or grooves which hold them in place.
Conventional connectors designed for connection to printed circuit boards are not completely satisfactory for another important reason. Thus, digital-based electronic equipment, such as computers, are a major source of electromagnetic (EMI) and radio frequency (RFI) interference emission. Such interference has become a problem at least in part due to the reduction in size of components and printed circuit boards, the increased speed at which data is being transmitted, and the movement away from metal and towards plastic as the material from which the plug housings are formed. Plastic materials generally lack the shielding capabilities which are inherent in metal housings. The increased growth in the use of printed circuit boards has aggravated the situation by creating potentially serious problems with EMI and RFI and this, in turn, has had a direct influence on household use of radios, televisions etc., and other electrical appliances.
In order to prevent or at least substantially reduce the emission of interference-causing electromagnetic and radio frequency radiation from multi-conductor cable used in digital-based electronic equipment and to provide at least some protection from interference-causing signals radiated from external equipment, cables have conventionally been provided with "shielding" in the form of a continuous sheath of conductive material situated between the outer insulation jacket of the cable and the insulated conductors, which sheath surrounds and encloses the conductors along their length. The shield can be formed of any suitable conductive material such, for example, as thin Mylar having a surface coated with aluminum foil or thin conductive filaments braided into a sheath construction. The cable shield acts to suppress or contain the interference-causing electromagnetic and radio frequency signals radiating outwardly from the cord conductors and, conversely, to prevent such high frequency signals generated by external equipment from causing interference in the conductors.
However, these techniques have not satisfactorily eliminated the interference problem and have created additional problems. Specifically, it has been found that electromagnetic and radio frequency radiation emission occurs in the region of the connector, i.e., in the region at which the plug is inserted into the jack. Moreover, it is not uncommon for high frequency signals radiated from nearby equipment to pass through the jack and cause interference in the cord conductors.
Furthermore, the cable shield tends to acquire an electrostatic charge over a period of time and provisions therefore must be made to ground the shield. This has conventionally been accomplished either by means of a so-called "drain wire" which extends through the cord in electrical engagement with the conductive shield, the end of the drain wire passing out of the plug for connection to ground, or by grounding the cable shield through one of the plug contact terminals designed to engage a grounded jack contact upon insertion of the plug into the jack. However, when the radiation shield is grounded using such conventional techniques, it is not uncommon for deleterious electrical discharge arcs to occur across the connector contacts or across the printed circuit board conductors. Such arcing can cause serious damage to the electrical equipment.
The applicability of modular type connector to digital-based electronic equipment has in the past been limited by the geometry of the electronic equipment and conventional plugs and jacks. Such equipment often comprise components which include a plurality of printed circuit boards stacked one over the other in closely spaced overlying relationship. For example, a computer may have printed circuit boards stacked one over the other with adjacent boards being spaced no more than one-half inch from each other. Since a typical printed circuit board has a thickness of about 0.060 inches and the pin portions of a jack connected to the board should protrude about 0.060 inches below the bottom of the board to permit effective soldering connections, an inter-board space of only about 3/8 inch would be available to accommodate a jack for receiving a plug. Indeed, this dimension may be even somewhat less where the jack is enclosed within an insulating sleeve to prevent electrical engagement with the jack pin portions protruding from the bottom of the next adjacent printed circuit board.
Since the height of conventional modular type plugs is already about 3/8ths inch, the use of such connectors in environments of the type described above, keeping in mind the necessity of providing a jack for receiving the plug, is clearly not possible.
Another practical disadvantage of conventional connector arises where the connectors are used to terminate cables having a relatively large number of conductors. In such cases the assembly of the plug creates problems in the management of the conductors, i.e., it becomes difficult to properly position each conductor in precise alignment for connection with a corresponding plug contact in a quick and reliable manner.
A modular plug connector and jack assembly is available from Amp Corp. under the designation Data Link U.S. Pat. No. 4,457,575 wherein the outer surfaces of the plug receptacle entrance end of the jack is enclosed within a cap-like member of conductive sheet metal having contact projections which extend around the front of the jack and into the receptacle entrance. The cap-like member has pin portions adapted to be connected to ground through a printed circuit board. The plug housing is surrounded by a conductive collar which extends through the cord-receiving opening of the plug to terminate the cord shield. When the plug is inserted into the jack receptacle, the contact projections extending into the receptacle engage the shield terminating collar. This arrangement is not entirely satisfactory since the EMI/RFI shielding for the plug and the electrical engagement of the shield terminating collar of the plug to ground the same are not sufficient and reliable under all circumstances. Moreover, the location of the contact projections within the plug receptacle of the jack restricts the extent to which the profile of the jack can be reduced.